20 Cutler, Parthenogenesis in Animals 



maturation and reduction, we must assume that the female 

 element has been eliminated, but by hypothesis the spermatozoa 

 at fertilisation must bring into the egg the female tendency. It 

 is difficult to see howl thjs is 'possible. Castle offered! a solution 

 by pointing out that the testes Were developed from the fused 

 polar bodies, and that therefore they would contain the female 

 element. We have seen, ' however, that this observation of 

 Petrunkewitsjch is incorrect. A second theory due to Correns is 

 based On experiemnts performed with Bryonia. The assumption 

 here is that the male is heterozygous for sex, but the female 

 homozygous. The difficulty of selective fertilisation is by this 

 means overcome, for it is obvious that either a male or a 

 female sperm can fertilise the ova, which' in this case are all 

 alike in character. The bee again offers difficulties, for the par- 

 thenogenetic females must bear male tendencies, but according 

 to the theory they lack them. Beard has suggested that this 

 can be explained by assuming two types iof eggs, sexual female- 

 producing type, which must be fertilised, and male- producing 

 type, where the female tendency is replaced by a latent male 

 tendency. The assumption of a latent male tendency seems to 

 me, however, to be too speculative in nature to warrant accept- 

 ance. A reversal of Correns' formula sen that the females are 

 heterozygous and the male homozygous offers the same kind of 

 difficulties, for, , as in the Castle theory, the female tendency {is 

 eliminated at maturation of the parthenogenetic egg, and yet the 

 sperm brings into the egg that tendency. 



In the foregoing brief account of these theories of sex I have 

 given very few objections to them, but reference to the literature 

 of the subject will at once demonstrate that the difficulties are 

 very numerous and are sufficiently great to warrant scepticism 

 before they are accepted. Doncaster has formulated another 

 view, in which it is supposed that the female is heterozygous for 

 sex but that the male produces two kinds of spermatozoa, one of 

 which contains a male determinant, but the other lacks any deter- 

 minant for sex. The difficulty of accounting fo>r the facts 

 observed in the bees, etc., again arises. 



Doncaster suggested that the presence of a sperm in the egg 

 influences the maturation in such a way as to cause normal 

 maturation to occur. Then the chromosomes are halved both 

 quantitatively and qualitatively and the male determinant is 

 eliminated. If the egg maturates without fertilisation the female 

 determinant is removed. In this way the spermatocytes contain 

 a single male determinant which passes into one spermatid, 

 leaving the other without any determinant. This latter is the 

 abortive bud which degenerates. All spermatozoa then contain 

 the male determinant and after fertilisation the sperm by its 

 presence causes the male •determinant of the egg to be eliminated. 



